Immunohistochemical staining of a fetal ovary specimen, gestation week 40. Hematoxylin-eosin (HE) staining (panels A, G, M) and immunohistochemical staining with mAbs MA454 (panels B, H, N), M3H67 (panels C, I, O), 57B (panels D, J, P), CT7-33 (panels E, K, Q), and ES121 (panels F, L, R) are shown. Dense primordial follicles with central oocytes (panels G, M; stars) surrounded by distinct follicle epithelial cells (panels G, M; arrows) are seen. No immunohistochemical staining is observed with mAbs MA454 (panels B, H, N) and ES121 (panels F, L, R). Focal primordial follicles with immunopositive oocytes are seen with mAbs M3H67 (panels C, I, O), 57B (panels D, J, P), and CT7-33 (panels E, K, Q) which display single intensely immunostained germ cells (exemplified in panels I, O; stars); foci of CT7-33-positive oogonia without follicle formation (panels K, Q; arrows) and single positive oocytes (panels K, Q; stars) are visible. Objective magnification: 10x (panels A - F), 20x (panels G - L), 40x (panels M - R).